A 2015 Gmc Yukon presented with a check engine light (CEL) and a prolonged crank time during startup. Despite these symptoms, the vehicle exhibited no noticeable drivability issues. Interestingly, the Yukon had recently undergone an engine replacement, approximately 400 miles prior, with a Jasper Engines 6.2L unit. This new engine was installed with an Active Fuel Management (AFM) delete, utilizing a TDN tuner and a preloaded tune to accommodate this modification. The original engine failure stemmed from a collapsed AFM lifter, causing camshaft lobe damage and significant metallic debris throughout the engine. Following the engine replacement, the vehicle operated without issues until the recent appearance of the CEL and extended cranking.
The primary anomaly observed during diagnosis was the “camshaft active counts” live data parameter, which remained almost static. While the “crankshaft active counts” registered normally, the camshaft counts rarely incremented, occasionally flickering with a mere one or two dozen counts. Suspecting a faulty camshaft position sensor, a Picoscope 4425A was employed to examine the sensor waveform. The initial waveform revealed minor clipping at the peaks of some teeth. Consequently, the camshaft position sensor was replaced.
Post-replacement, the waveform clipping was resolved, yet the long crank issue and related diagnostic trouble codes persisted. A cam/crank synchronization test, performed using the Picoscope, showed alignment consistent with known good waveforms from comparable vehicles and online resources. Unfortunately, the waveform capture is not currently available, but a pre-replacement image illustrating the sensor clipping is included above. The uncertainty lies in whether the camshaft-related code is inhibiting the active counts in the live data, or if an ECM malfunction or a peculiarity within the AFM delete tune is responsible.
Retrieving the tuner to revert to the stock ECM programming is proving difficult. The technician who performed the initial installation could not locate the tuner, suggesting it may have been discarded or inadvertently left in the customer’s vehicle, which is also now untraceable. While OEM GM programming software is available to force a flash back to the factory settings, this would necessitate repurchasing a tuner to reinstate the AFM delete tune, which is undesirable at this stage of diagnosis.
Further troubleshooting steps have been somewhat constrained. All power, ground, and communication signals to and from the camshaft position sensor at the ECM connectors have been verified as within specification using piercing probes while the fault condition was present. Furthermore, acting on Jasper Engines’ recommendations, both the camshaft position sensor and the camshaft actuator magnet (the three-bolt solenoid controlling timing with a two-wire connector) were replaced with genuine OEM GM parts, despite showing no apparent defects during testing. Jasper has also proposed replacing the camshaft gear itself and, if concerns remain about this procedure, have offered a complete engine assembly under warranty.
Before proceeding with ECM replacement or tuner repurchase, additional insights or experiences with similar issues are being sought. Specifically, information regarding AFM deleted Jasper engines and their associated tune software is of interest. It is crucial to determine if the tune configuration might intentionally suppress camshaft active counts in the ECM data stream, thereby causing the observed PID (Parameter ID) malfunction. Any guidance or suggestions before considering a new or remanufactured ECM would be greatly appreciated, as this represents a more cost-effective and quicker solution than acquiring a replacement tuner for the missing unit.
